This invention relates to a control apparatus for a hybrid vehicle having an electric motor directly connected to an engine and having both driving and power-generating functions. A main battery supplies a driving electric power to the motor and is charged by power-generating electricity from the motor. The control apparatus controls the motor functions and administers the battery.
Some motor vehicles are of a type commonly called hybrid vehicles having an internal combustion engine which is driven by combustion of fuel and an electric motor (hereafter described as xe2x80x9cmotorxe2x80x9d) driven by electric energy, wherein the motor is directly connected to the engine and has a power-generating function. The hybrid vehicle further includes an engine control means for controlling a running state of the engine and motor control means for controlling an operating state of the motor. The engine control means and the motor control means detect respective operating states of the engine and the motor when the vehicle is traveling, and then exchange such detected data regarding the running states. As a result, the respective operating states of the engine and the motor are controlled in association with one another. Such a control system attains a high level of required performance (such as fuel efficiency, low values of detrimental components in exhaust gases, and power performance). The apparatus includes a main battery which supplies drive electricity to the motor and is charged by power-generation of the motor. A required voltage for the main battery must be maintained to enable suitable driving power-generation/driving prohibition for the motor. This apparatus administers control of the battery.
One such example of a control apparatus for a hybrid vehicle is disclosed in published Japanese Application Laid-Open No. 11-136808. In the hybrid vehicle of this disclosure, the control apparatus has a battery state distinguishing means and a power-generation electricity determining means which prevent over-charge and over-electric discharge of a main battery, and which control power-generating of electricity to satisfy essential power performance requirements of a vehicle.
A control apparatus of a traditional hybrid vehicle maintains a reasonable charge state in a battery. For this purpose, the control apparatus detects various parameters such as water temperature, electric current, voltage and so on, and decides how to control a motor from the detected results. Accordingly, there is a problem or inconvenience in that a system to administer the battery becomes complicated and expensive in hardware and software.
In order to obviate or minimize the above problem, the present invention provides a control apparatus for a hybrid vehicle, which includes an electric motor directly connected to an engine and having both driving and power-generating functions, and a main battery which supplies driving electric power to the motor and is charged by power-generating electricity from the motor. A control means has a normal control mode which detects the battery open-circuit voltage of the battery at driving stop of the motor, and which sets voltage parameters according to the battery open-circuit voltage. In addition, the motor control means has an electric discharge control mode which sets a value of a battery voltage parameter to a fixed value when the battery open-circuit voltage is higher than values for the normal control mode.
In this invention, motor control means has a normal control mode which detects the battery open-circuit voltage of the main battery at driving stop of the motor and sets voltage parameters according to the battery open-circuit circuit voltage. In addition, the motor control means has an electric discharge control mode which sets a value of a battery voltage parameter to a fixed value when the battery open-circuit voltage is higher than those at normal control mode. Accordingly, the voltage parameter is set at a value to cause an electric discharge tendency (giving priority to drive of the motor). When a battery state is good, the motor is driven only for a voluntary time period until an electric discharge of fixed quantity is used. As a result, fuel efficiency is improved, and driving performance is improved by the effect of motor assist. In addition, over-charge and over-electric discharge of the main battery can be prevented. Accordingly, by reasonable charge and electric discharge, the life of main battery is extended. Furthermore, battery administration can be performed with a simplified system of hardware and software.